1. Field of the Invention
The present invention relates to a focus stabilizing apparatus for stabilizing a focused state of an optical apparatus, such as a microscope.
2. Description of the Background Art
Generally, a sample observation is carried out with the use of a microscope. This sample observation is made as follows. An observation sample is placed on a microscope stage and an objective lens is moved closer to the observation sample. By doing so, an observation spot of the observation sample is observed under a magnified state.
In this case, an objective lens has its focal depth decreased as the magnifying power becomes higher. It is, therefore, difficult to achieve a focus setting between the objective lens and the observation sample. Further, if the distance between the objective lens and the observation sample minutely varies, defocusing occurs between the focal point position of the objective lens and the observation sample due to a variation of the minute distance, so that the quality of the observation image is greatly degraded.
On the other hand, an apparent position between the objective lens and the observation sample is very closer to each other. By the way, there exists a mechanical coupling length between the objective lens and the observation sample. This mechanical coupling length is constituted by many mechanical component parts present between the objective lens and the observation sample. The mechanical coupling length is provided by the length over which, for example, a microscope frame, objective lens moving mechanism, objective lens mounting revolver are passed. Therefore, the length is very long because many mechanical components are interposed.
These mechanical component parts are liable to be varied in their dimensions due to a temperature variation involved.
Further, the greater the number of the mechanical component parts the greater the mechanical coupling length involved. The microscope is easily affected by a vibration and the vibration amplitude becomes greater.
If, therefore, the ambient temperature varies due to, for example, the turning ON/OFF of an illumination, internal power supply, etc., as well as the operation of an air conditioning equipment, then there arises a variation in the dimensions of mechanical component parts in the microscope. Even if, therefore, the focal setting of the objective is made relative to the observation sample, the distance between the objective lens and the observation sample greatly varies due to the above-mentioned dimensional variation and there occurs a defocusing.
Further, under a somewhat smaller external vibration, a greater vibration amplitude is involved and a distance between the objective lens and the sample varies, thus resulting in an out-of-focus state.
Heretofore, various kinds of autofocusing mechanisms have been considered to compensate such defocusing. These autofocusing mechanisms require a complex mechanical/electrical mechanism and control system. For this reason, the resultant apparatus becomes bulkier and expensive. Further, another microscope is known in which, like a fluorescent observation, the brightness is extremely darker at a time of observation. To such a microscope it is originally difficult to apply the above-mentioned autofocusing mechanism.
The following technique is disclosed in JPN PAT APPLN KOKAI Publication No. 9-120030. In this technique, a stage is provided through a rack and drive gears and it is driven in the optical axis direction of the objective lens. Between the gears and the stage, at least two rods are inserted. These rods are different in their thermal expansion coefficients and configured such that the direction of the thermal expansion coefficient of one rod acts in a direction opposite to that of the other rod. By doing so, defocusing is compensated.
In such a technique, the rods are arranged within the microscope body and a time is taken until the temperature is compensated under a variation of the ambient temperature. For this reason, there is a risk that, when the sample is observed, its operation, efficiency will be lowered. Further, since the rods are interposed, the mechanical coupling length becomes greater and its structure is liable to be affected from the external vibration. It is, therefore, necessary to remodel the microscope itself.
In the case where a living cell, etc., is observed as a target object, only a periphery side of the observation sample is sometimes warmed by a warmer. However, it is not possible to compensate a temperature drift involved.